My next-door neighbor happens to own a Nikon D40, she is just learning how to get the most from it. I was walking by and happened to have my Sigma 50-150 attached to mine. I demonstrated the art of shooting available-light imaging by taking a photo of her 4-year-old daughter. This was done at ISO 1600, wide-open, about 1/30th second. It's barely sharp, but it shows that a fast lens can do this sort of thing and capture the mood.